DESCRIPTION: The epidemiology of breast cancer is complicated and only partially understood, despite a concerted research effort in this area. The primary goal of the proposed study is to examine the association between, on the one hand, perinatal factors that exhibit their hypothesized carcinogenic action during early life and, on the other established breast cancer risk factors that operate during the perimenarcheal years. Our objective will be to explore whether certain perinatal factors may share a common biologic mechanism of action with perimenarcheal risk factors, with respect to breast carcinogenesis. The meet this objective, the following specific aims will be addressed to investigate if there is an association between birth size and indicators of sexual maturity during adolescence, particularly age at menarche and breast development; to study the association between birth size and adolescent somatic growth; to examine the association between perinatal complications, such as pregnancy pre-eclampsia/eclampsia, jaundice, and prematurity, and indicators of sexual maturity and somatic growth during adolescence. To study these relationships, a retrospective cohort study of the association between perinatal and adolescent factors will be conducted among young girls in Nord Trondelag County in Norway. The population based for this study will be the nearly 5,000 girls, 13 to 19 years of age, who were born between 1977 and 1984 and who participated in general health survey for adolescents that took place in 1996 and 1997. Using the unique personal registration number assigned to all Norwegians, linkage will be made between the relevant information collected during the adolescent health survey and birth record information stored in the national Birth Registry. Access to data of such excellent quality will provide an important opportunity to examine the role of perinatal and perimenarcheal factors in the etiology of breast cancer.